A. Field of the Invention
The present invention relates to a double side scanner module, especially to a scanner module consisting of a U-shaped inversion device, and two image information reading devices, thereby to read the images on both sides of an original in a single pass.
B. Description of the Prior Art
A conventional scanner or facsimile machine can only scan one side of an original. If a user wants to scan two sides of an original, he has to manually turn over the original to the other side and scan the original once again. To provide a scanner with the functions of double side scanning, an U.S. Pat. No. 4,743,974, “Dual Scanning Array Raster Input Scanner” by Dan F. Lockwood disclosed a scanner which uses two Charge Coupled Devices (CCD) disposed face to face so as to read the images on the two sides of an original in a single pass.
Refer to FIG. 1, two CCDs 11, 12 are located face to face with two pieces of glass windows 13a, 13b interposed therebetween. The structure as illustrated in FIG. 1 is a multi-mode scanner. In a first mode, if the user only wants to scan one side of an original, he may put the original on the sheet table 15. Then, the lower CCD 12 will be driven by the guiding shaft 14 to move along the sheet table 15 and progressively read the entire image of the original. In a second mode, if the user wants to scan both sides of an original, the original will be conveyed by the roller set 16 to pass through the two glass windows 13a, 13b. Consequently, the two CCDs 11, 12 can almost simultaneously read the images on the two sides of an original.
In practice, it would be difficult for the invention of Lockwood to avoid the shadows caused by the fluorescent light emitted from the two face-to-face CCDs 11, 12 even though Lockwood taught that the two CCDs 11, 12 shall be arranged biased with an offset. For one thing, since the two CCDs 11, 12 read the image information almost simultaneously, they cannot be located far apart. In other words, they must be arranged closely enough to be able to read the entire page without missing the image on the front end or the lower end. In that case, the fluorescent light emitted by the two CCDs 11, 12 is so strong that the shadow effects can hardly be avoided according to the structure as illustrated in FIG. 1. Moreover, the scanner module of Lockwood is too complicated to be implemented inside a small image reading apparatus, such as a scanner or a facsimile machine.